Autoimmune diseases have been the subject of widespread press attention because of the considerable morbidity worldwide that they cause. Autoimmune diseases include rheumatoid arthritis, type-1 diabetes mellitus (insulin dependent), multiple sclerosis, myasthenia gravis, systemic lupus erythematosus, Sjogren's syndrome, mixed connective tissue disease, experimental allergic encephalomyelitis (EAE), to name a few. Considerable research has been expended and is currently underway in order not only to devise a treatment or prophylaxis against such devastating diseases, but also to study the underlying etiology(ies) such that a better understanding can be gained as to common denominators, if any, that would more directly focus a plan of attack for conquering them.
In most cases, it is believed that autoimmune diseases result from abnormal cells of the immune system destroying target tissues, either by direct killing or by producing autoantibodies. One may focus for exemplification on historic autoimmune diseases. One such is the so-called systemic lupus erythematosus (SLE). In SLE, abnormal B-lymphocytes produce anti-DNA antibodies that are positively charged and aggregate on negatively charged kidney cells causing inflammation and nephritis, which is symptomatic of SLE. In diabetes mellitus, abnormal T cells systematically destroy pancreatic islet cells such that they prove incapable of producing insulin, a necessary hormone for proper metabolic balance in an organism. In multiple sclerosis, abnormal T cells are believed to damage myelin basic protein, a major component of nerve cells, which systematically destroys certain nerve cells, causing a spectrum of neurological symptoms. In the autoimmune diseases studied to date, there seems to emerge a common pattern of abnormal immune system cells producing materials that either destroy or retard certain target tissues causing symptoms manifest for that disease state.
Current treatment for these diseases remains on an empirical level and is based on causing generalized immunosuppression, either with steroids or other immunosuppressive drugs. This therapeutic approach is also fraught with other problems including associated severe side effects. Further, they serve only to retard the natural progression of these autoimmune diseases. Effective therapeutic treatment, to say nothing of a cure, is beyond present day medical technology. The aberrations in the immune system resulting in these various autoimmune diseases are not well understood, despite the extensive research that has taken place in this field. See Theofilopoulos, et al., Adv. Immunol. 37, 269 (1985), for example.
Research has focused on the use of various murine models that have provided considerable insight into the pathogenesis of the disease states, although the clinical syndromes and immunological abnormalities vary considerably from strain to strain, making them less than perfect studies. Thus, a common underlying cellular or molecular defect that is common to all these diseases has not been identified, if indeed there is even a suggestion in the extant art that one exists.
Studies by several investigators have demonstrated that injection of antibodies against CD.sub.4.sup.+ CD.sub.8.sup.- T cells prevents, and in some cases retards, the onset of certain autoimmune diseases in certain murine models. See Theofilopoulos, et al., Adv. Immunol. 37, 269 (1985); Wofsy, et al., J. Exp. Med. 161, 378 (1985); Wofsy, et al., J. Immunol. 136, 4554 (1986); Wofsy, et al., J. Immunol. 134 852 (1985); Santoro, et al., J. Exp. Med. 167, 1713 (1988); Waldor, et al., Science 227,415 (1985); Ranges, et al., J. Exp. Med. 162, 1105 (1985); Christadoss, et al., J. Immunol. 136, 2437 (1986); and Sriram, et al., J. Immunol. 136, 4464 (1986). This treatment also results in the reduction of a subpopulation of CD.sub.4.sup.- CD.sub.8.sup.- T cells. In cumulative effect, these data may point to a common underlying mechanism mediated by CD.sub.4.sup.+ CD.sub.8.sup.- T cells and/or CD.sub.4.sup.- CD.sub.8.sup.- T cells. See Santoro, et al., J. Exp. Med. 167, 1713 (1988).
Existing evidence may further suggest reasons attending the role CD.sub.4.sup.- CD.sub.8.sup.- T cells play in the induction of SLE, for example. First, these cells from diseased SLE mice induce B cells to secrete pathogenic anti-DNA autoantibodies in vitro, whereas the same cells from normal mice or from pre-autoimmune mice do not exhibit this property. Datta, et al., J. Exp. Med. 165, 1252 (1987); Sainis, et al., J. Immunol. 140, 2215 (1988). Second, the onset of SLE is greatly accelerated in mice that have a severe lymphoproliferation of such cells due to the expression of the autosomal recessive mutations lpr or gld. See Theofilopoulos, et al., supra. Third, patients with SLE nephritis have an expanded CD.sub.4.sup.- CD.sub.8.sup.- T cells population in their blood that induces secretion of autoantibodies. Shivakumar, et al., FASEB J. 3, A492 (No. 1548) (February, 1989) and Datta, Federation of American Societies for Experimental Biology Summer Conference on Autoimmunity at Saxton's River, Vt., Jul. 3-8, 1988. Cumulatively, these data may suggest that CD.sub.4.sup.- CD.sub.8.sup.- T cells mediate in some fashion autoimmune disease, contributing to the development of the disease. However, thus far, no marker or alteration or aberration that is unique to the abnormal CD.sub.4.sup.- CD.sub.8.sup.- T cells related to autoimmunity, has been identified.
It was previously reported that K.sup.+ channel expression in proliferating CD.sub.4.sup.- CD.sub.8.sup.- T cells from mice with lpr mutations was dramatically altered. Chandy, et al., Science 233, 1197 (1986). That research resulted in the association of an abnormal pattern of ion channel expression with an SLE prone genetic defect in cells of the immune system, associated with abnormal lymphoproliferation.
The next step was to determine whether the same abnormal expression pattern could be observed for cells from mice that were not genetically predisposed to SLE, as were the murine models of Chandy, et al., supra. Thus, in Grissmer, et al., Journal of Immunology 141, 1137 (1988), murine models that were not prone for SLE, developed similar abnormal expression patterns associated with the onset of SLE and lymphoproliferation. Thus, while in Chandy, et al., supra., abnormal overexpression of type l K.sup.+ channels in SLE prone murine models was thought to be a lpr mutation dependent abnormality of the immune system, in Grissmer, et al., Supra, similar proliferation of type l K.sup.+ channels in mice with two distinct mutations (lpr and gld) indicated either that such overexpression was somehow associated with SLE itself or to simple lymphoproliferation symptoms. See also Lewis, et al., Science 239, 771 (1988) and DeCoursey, et al., Nature 307,465 (1984).
Theofilopoulos, et al., in Advances in Immunology 37, 269 (1985), a review article, suggest that the disease profile in the lpr and gld murine models does not resemble any known variant of human SLE. Theofilopoulos, et al. suggest that a clear correlative model is necessary.
Thus, missing in the art is information necessary to establish unequivocally whether, and if so how, abnormal immune cell proliferation and ion channel expression is related etiologically to autoimmune diseases.
Present attention focused on the ion channels themselves. Three types of ion channel types, classified pharmacologically and electrophysiologically, were identified, the so-called n, n' and l types. T cells in the peripheral lymphoid tissues for present purposes, are characterized into relevant types: CD.sub.4.sup.+ CD.sub.8.sup.-, CD.sub.4.sup.- CD.sub.8.sup.+, CD.sub.4.sup.- CD.sub.8.sup.-. The CD.sub.4.sup.+ CD.sub.8.sup.- cells are thought to express approximately 20 n channels per cell and are believed to have no n' and l channels. CD.sub.4.sup.- CD.sub.8.sup.+ +T cells are thought to have about 20 n' and l channels per cell and no n channels. And CD.sub.4.sup.- CD.sub.8.sup.- T cells are believed to express about 20 channels per cell, all three types being represented. In a normal immune response reflecting induction of activity, such as with mitogens, the n channel types are increased upwards of ten-fold in the cells that are activated. Thus, normal T cells when stimulated by mitogens, show as a normal immune response elevation in the number of n channels. Blocking these n channels, for example with tetraethyl ammonium (TEA), would serve to shut down and effectively block an immune response. Abnormal T cells may also be subject to a similar blockage. However, such abnormal T cells are represented by CD.sub.4.sup.- CD.sub.8.sup.- cells, manifesting a proliferation of type l channels. Type l K.sup.+ channels are not use dependent, close more rapidly on repolarization than do n channels and are much more sensitive to blockage, for example by TEA. It was the unsuggested goal of the present research to establish a link, if any, hence an etiology, between abnormal ion channel expression in immune cells and systemic symptoms of autoimmune disease states. A further goal of the present research was to isolate and characterize the nucleic acid sequences which encode the type l K.sup.+ channel.